Blended hydrous kaolin clay product

ABSTRACT

The disclosed invention relates to a blended hydrous kaolin clay product comprising a platy coarse kaolin clay and a fine, hydrous kaolin clay. The blended kaolin clay product is suitable for use as a raw material component in the formation of cordierite products.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.12/543,228, filed Aug. 18, 2009, issued as U.S. Pat. No. 8,129,302 onMar. 6, 2012, which in turn claims benefit under 35 U.S.C. §119(e) ofU.S. provisional application U.S. Ser. No. 61/090,024, filed Aug. 19,2008, each of whose contents are incorporated herein by reference intheir entireties.

FIELD OF THE INVENTION

This invention is related to a kaolin product as a raw product for usein specialized applications. In particular, this invention is related toa blended hydrous kaolin clay product for use as a raw materialcomponent in the formation and sintering of cordierite ceramichoneycombs with enhanced thermal properties.

BACKGROUND OF THE INVENTION

Cordierite (Mg₂[Al₄Si₅O₁₈]) ceramics are the preferred materials for usein automotive catalytic substrates, diesel particulate filterapplications, and other high temperature articles, such as NO_(x)adsorber substrates, catalyst substrates, and honeycomb articles due tothe combination of their low cost of production and physical propertiessuch as low coefficient of thermal expansion (CTE) and resistance tothermal shock.

Cordierite substrates are typically produced from naturally occurringminerals such as talc and kaolin due to their lower cost and highpurity. Cordierite materials are typically manufactured by mixing a rawbatch that includes talc, alumina, aluminum hydroxide, kaolin andsilica. The batch is then blended with a binder (such asmethylcellulose) and a lubricant (such as sodium stearate) to form aplastic mixture. This plastic mixture is then formed into a green bodyand sintered.

The cordierite crystal structure consists of a hexagonal ring oftetrahedra that are joined at each intersection of the hexagonal ring byfive silicon and one aluminum atom. The hexagonal rings are connectedtogether by additional aluminum tetrahedral and magnesium octhedraresulting in two interstitial vacancies per unit cell that are orientedalong the c-axis of the crystal structure. See, B. P. Saha, R. Johnson,I. Ganesh, G. V. N. Rao, S. Bhattacharjee, T. R. Mahajan; MaterialsChemistry and Physics, 67 (2001), 140-145. The interstitial vacanciesresult in a contraction along the c-axis of the crystal structure and anexpansion along the a- and b-axes with increasing temperature. See, R.J. Beals, R. L. Cook, J. Am. Ceram. Soc., 35(2), (1952), 53-57. Theanisotropic CTE resulting from the cordierite crystal structure offersthe opportunity to engineer improved cordierite honeycombs by orientingthe c-axis of the individual crystals within the Ceramic in thedirection of extrusion. Cordierite crystal orientation has been observedto cause a significant net decrease in the overall CTE of the ceramichoneycomb. See, I. M. Lachman, R. M. Lewis, U.S. Pat. No. 3,885,977, May27, 1975; and R. Johnson, I. Ganesh, B. P. Saha, G. V. Narasimha Rao, Y.R. Mahajan, J. Mater. Sci., 38 (2003), 2953-61.

In order to orient the cordierite crystals within the ceramic, platy rawmaterials are used. In particular, talc and kaolin have platy crystalstructures that may be preferentially oriented parallel to the directionof extrusion when passed through an extrusion die at high pressure.Delamination of hydrous kaolin may be utilized to increase the platynessof the clay increasing alignment during extrusion. Subsequent sinteringof the green body results in the formation of a ceramic withpreferential orientation of cordierite crystals within the honeycombstructure oriented along the c-axis relative to the extrusion direction.See, I. M. Lachman et al., U.S. Pat. No. 4,772,580, Sep. 20, 1988.Although talc and kaolin both play a role in orienting the sinteredcordierite crystal structure, kaolin is considered to be the mostsignificant contributor because it provides the only source of orderedaluminum within the green body. Since silicon comes from both talc andkaolin raw material sources and magnesium (talc as the source) makes upa smaller atomic and weight percent of the final cordierite crystal,aluminum (derived from kaolin) is expected to have the greatestcontribution to the final cordierite crystal structure. See, Saha et al.

One drawback with producing a highly ordered cordierite substrate isthat the difference in thermal expansion along the axial and transversedirections in the honeycomb becomes so large that cracking occursresulting in reduced thermal shock resistance. See, Saha et al. Althoughthis is a concern for catalyst substrates, it is of particularsignificance to honeycombs produced for diesel particulate filterapplications where increased porosity lowers the shock resistance of theresulting ceramic. In addition, the extrusion of highly oriented rawmaterials parallel to the axial direction of the substrate lowers thestrength of the green body resulting in sagging of the body,particularly in thin wall applications. To alleviate these problems,calcined clay is typically added in combination with delaminated hydrousclay to moderate particle alignment within the green body and subsequentcordierite crystal alignment within the sintered ceramic. Calcinationproduces a coarser particle that is less platy in nature particularlycompared to delaminated hydrous clay.

SUMMARY OF THE INVENTION

This invention is directed to a blended hydrous kaolin clay productcomprising a platy kaolin clay with a mean particle size of less thanabout 2 um in diameter, and a fine hydrous kaolin clay with a meanparticle size less than about 1 um in diameter. In an embodiment, theplaty kaolin clay is a delaminated kaolin clay. The resulting clayproduct can be used as a raw material component in the formation andsintering of cordierite substrates, for example, ceramic honeycombs. Theparticle size of the kaolin clay may be measured by a MicromeriticsSedigraph Model 5100 instrument.

This invention is also directed to a method of forming a blended hydrouskaolin clay product, the method comprises blending clay mined fromtertiary crude deposits as the fine component; and Cretaceous orsecondary clay. The blended kaolin clay product comprises tertiarykaolin where about 75% or more of the total particle mass is less thanabout 2 um and more than about 55% of the total particle mass is lessthan about 1 um and would be suitable for improved cordieriteproduction. It comprises mixing a coarse component containing less than85% of the total particle mass less than about 2 um with a tertiary finecomponent where 95% or more of the mass of the sample is less than about1 um and more than 85% of the sample is less than about 0.5 um inparticle size.

DETAILED DESCRIPTION OF THE INVENTION

This invention is related to a blended hydrous kaolin clay product thatcan be used as a raw material component in the sintering of cordieriteceramic honeycombs with enhanced thermal properties. The blended productis composed of a coarse, platy, hydrous kaolin clay and a fine hydrouskaolin clay. The combination of these two materials is expected toenhance the thermomechanical properties of cordierite honeycombs bycreating a mechanism to manipulate the degree of cordierite crystalorientation in the final product.

The use of fine clay in combination with a larger delaminated clay wouldhave several advantages. The fine clay could be used to moderateorientation of the delaminated kaolin and talc during extrusionresulting in a cordierite crystal structure that is oriented to maintaina low coefficient of thermal expansion while minimizing the degree ofanisotropic thermal expansion in the axial and transverse directions ofthe ceramic honeycomb. This would reduce the degree of microcrackingassociated with temperature variations typically observed during normalcatalytic converter or filtering operations. The fine particle size clayalso enables improved particle packing within the green body. The finerhydrous clay would fill voids between other larger raw material crystalsthat calcined clay could not. The improved particle packing within thegreen body would increase the green strength eliminating productdeformation prior to drying and firing of the substrate.

It is desirable to have a more homogenous distribution of cordieriteprecursors within the green body which would potentially be enabled bythe addition of a fine hydrous kaolin component. Increased homogeneitywould enable improved conversion of the precursors into cordierite andlimit the formation of impurity phases within the crystal structure thatwould increase the coefficient of thermal expansion of the overallceramic. The increased surface area and reduced crystallinity associatedwith a finer, hydrous clay would also have a lower reaction temperaturethat would enable reduced temperature or firing time of the substratewithout impacting the overall conversion to cordierite. This wouldreduce the energy costs associated with product manufacture.

One embodiment of this invention is the use of a platy (but notnecessarily delaminated) coarse, hydrous kaolin component in combinationwith a fine, hydrous kaolin component. In this embodiment, the finekaolin would serve the same function of moderating platelet orientationduring extrusion of the cordierite-forming blend, but if anon-delaminated coarse component is used, then the ratio of the finecomponent relative to the coarse component would be reduced tocompensate for using a non-delaminated (less platy) coarse component.

In another embodiment of the invention, a blended hydrous kaolin clayproduct consists of a blend of (1) a delaminated hydrous kaolin claywith a mean particle diameter of less than about 2 um (the coarse kaolincomponent), and (2) a fine hydrous kaolin clay with a mean particlediameter of less than about 1 um (the fine kaolin component). Theparticle sizes have been measured using a Micromeritics Sedigraph Model5100 instrument. The weight ratio of the coarse kaolin component to thefine kaolin component can be in the range of from about 10:90 to about90:10 or, alternatively, in the range of about 50:50 to about 90:10 or,alternatively, in the range of about 70:30 to about 90:10. The preciseselection of the weight ratio of the coarse kaolin component to the finekaolin component will depend on the composition sought in the finalproduct (i.e., the precise ratio of the kaolin blend will depend on theother raw materials and the precise amounts which comprise the batchused in making the cordierite), and the desired properties of the finalproduct (e.g., improved coefficient of thermal expansion, improveddimensional accuracy, reduced tendency toward cracking, overallporosity, and pore size). A person skilled in the art would know,without undue experimentation, the ratio of the coarse to fine kaolincomponents needed depending on the other raw materials used in makingthe cordierite. The blending of the coarse and fine kaolin componentscould take place at any point during the mining and processing of theclay. This includes mixing the individual crude components duringinitial makedown, prior to spray drying, after spray drying, or as aproduct in slurry form. The coarse and fine kaolin components could alsobe added to the cordierite raw materials batch as individual componentsas long as the net result is the addition of two kaolin components thatwould form a blend with the properties outlined in this document.

Another embodiment of the invention is the use of clay mined fromtertiary crude deposits as the fine component of the blend incombination with a Cretaceous or secondary clay. Kaolin crudes havephysical properties that reflect the time period in which they wereformed. Tertiary crudes are typically finer in size, have differenttrace elemental profiles such as higher Fe₂O₃ content, and have higherdensities than clays deposited at other time periods. Tertiary clayconsists of Cretaceous clay (originally deposited 65 to 136 millionyears ago) that was eroded and redeposited 37 to 53 million years ago.Blends consisting of coarse and tertiary kaolin that are finer than 75%at 2 um and 55% at 1 um, respectively, as measured by a Sedigraph 5100would be suitable for improved cordierite production. Blended samplesmeeting these criteria have been produced by mixing a delaminated,coarse component, in which less than 85% of the total particle mass isless than about 2 um, with a tertiary fine component, in which 95% ormore of the mass of the sample is less than about 1 um and more than 85%of the fine component sample is less than about 0.5 um in particle size.Impurity profiles for the blended kaolin samples containing <about 0.1%Na₂O, <about 0.25% K₂O, <about 1.75% TiO₂, <about 0.6% Fe₂O₃, <about0.1% CaO, and <about 0.1% P₂O₅ should be met in order to produce highperformance cordierite.

Example 1

Example 1 contains several samples produced from blends of fine particlesize kaolin and coarse, delaminated kaolin streams obtained from BASF'skaolin manufacturing operations. The coarse delaminated streams arederived from two different sources of coarse, white clays in the MiddleGeorgia area. These samples are labeled Coarse #1 and #2. Coarse sample#1 (˜56% solids) was delaminated, flocked with acid and alum, filteredand redispersed with a polyacrylate dispersant. Coarse sample #2 (˜54%solids) was delaminated and did not require further processing otherthan addition of polyacrylate because of high solids processing. Thefine clays consisted of a tertiary kaolin (T1) mined from the MiddleGeorgia area and a tertiary kaolin (T2) mined from the East Georgiaarea. Both of the tertiary kaolins were flocked with acid and alum,filtered, and redispersed with a polyacrylate dispersant. The individualsamples were produced by blending the delaminated and fine particle sizekaolin streams. Sample #1 contains a 90% by weight blend of Coarse #1and 10 wt % of T1. Sample #2 contains a 90 wt % of Coarse #2 and 10 wt %of T1. Sample #3 contains 90 wt % of Coarse #1 and 10 wt % of T2. Sample#4 contains 90 wt % of Coarse #2 and 10 wt % of T2. Table 1-1 containselemental analysis of the four blended samples produced. Table 1-2contains the particle size distributions of each of the blends as wellas the coarse, delaminated and fine, hydrous kaolin components used.

TABLE 1-1 Sample ID % SiO₂ % Al₂O₃ % Na₂O % K₂O % TiO₂ % Fe₂O₃ % CaO %MgO % P₂O₅ % SO₃ % LOI Sample 1 44.5 39.2 0.041 0.13 1.30 0.43 0.03 0.030.06 0.04 14.2 Sample 2 44.3 39.4 0.019 0.05 1.39 0.31 0.04 0.02 0.060.03 14.3 Sample 3 43.8 39.9 0.042 0.13 1.29 0.45 0.03 0.03 0.05 0.0314.2 Sample 4 44.2 39.5 0.017 0.06 1.34 0.33 0.04 0.02 0.03 0.02 14.3Coarse #1 44.5 39.2 0.054 0.13 1.38 0.38 0.03 0.03 0.04 0.07 14.0 Coarse#2 44.6 39.2 0.024 0.04 1.48 0.24 0.04 0.02 0.07 0.04 14.1

TABLE 1-2 PSD Sample 1 Sample 2 Sample 3 Sample 4 Coarse #1 Coarse #2 T1T2 % < 10 um 99 99 100 99 98 99 99 100 % < 5 um 98 96 97 96 90 95 99 98% < 2 um 83 81 83 81 79 73 98 98 % < 1 um 67 64 67 64 61 59 97 98 % <0.5 um 49 43 48 44 39 42 90 92 % < 0.2 um 23 20 23 21 17 20 52 20

Example 2

Example 2 contains another embodiment of the described invention. Theblend was produced with a fine, hydrous and a coarse, delaminated kaolinwith the blend ratio adjusted to increase the fine component. The samplewas produced using coarse, white kaolin that was delaminated prior toblending. The fine kaolin was derived from a tertiary kaolin crude minedfrom the Middle Georgia area that was flocked with acid and alum,filtered, and redispersed with a polyacrylate dispersant. Sample #5contains a 70% by weight blend of the coarse, delaminated clay and 30 wt% of a Middle Georgia Tertiary kaolin. Table 2-1 contains the elementalanalysis obtained from this sample and Table 2-2 shows the resultingparticle size distribution.

TABLE 2-1 Sample ID % SiO₂ % Al₂O₃ % Na₂O % K₂O % TiO₂ % Fe₂O₃ % CaO %MgO % P₂O₅ % SO₃ % LOI Sample 5 44.8 38.7 0.026 0.08 1.18 0.44 0.04 0.030.08 0.05 14.44

TABLE 2-2 PSD Sample 5 Coarse #2 T1 % < 10 um 99 96 100 % < 5 um 97 96100 % < 2 um 86 80 98 % < 1 um 72 60 98 % < 0.5 um 54 36 93 % < 0.2 um27 14 57

Example 3

In order to demonstrate the benefits of the invention to cordieriteformation, cordierite pieces were extruded and fired using the proposedblend (Sample 6) as compared to a coarse kaolin (Sample 7) and adelaminated kaolin (Sample 8). Table 3-1 contains physical property dataand Table 3-2 contains elemental analysis for the three kaolin samplesexamined. The particle size for each sample was measured via Sedigraphand the surface area was determined by BET. Elemental analysis on thekaolin samples was obtained using XRF.

TABLE 3-1 Sample 6 Sample 7 Sample 8 Surface Area (m²/g) 18.3 7.5 14.0PSD % < 10 um 100 83 99 % < 5 um 98 50 96 % < 2 um 87 23 78 % < 1 um 7613 59 % < 0.5 um 59 7 35 % < 0.2 um 23 2 11

TABLE 3-2 Sample Id: % SiO₂ % Al₂O₃ % Na₂O % K₂O % TiO₂ % Fe₂O₃ % CaO %MgO % P₂O₅ % LOI Sample 6 45.8 39.5 0.03 0.09 1.11 0.52 0.02 0.04 0.0514.8 Sample 7 46.1 39.7 0.02 0.09 0.96 0.26 0.02 0.02 0.03 14.1 Sample 845.7 39.5 0.02 0.06 1.51 0.30 0.03 0.03 0.05 14.4

The cordierite pieces were formed by mixing raw materials consisting ofeach individual hydrous kaolin sample, alumina Al₂O₃), (and talc(Mg₃Si₄O₁₀(OH)₂) in a method known to the skilled person. Samples ofcommercially available high purity tale (Sample 13) and alumina (Sample12) for cordierite applications were used and the typical properties arelisted in Tables 3-3 and 3-4. No organic additives were used to form theraw batch. The water content of the batch ranged from about 32 to about36% in order to provide the plasticity necessary to extrude thematerial. The kaolin, alumina and talc precursors were blended in aratio to form stoichiometric cordierite with Sample 9 being formed fromSample 6, Sample 10 from Sample 7, and Sample 11 from Sample 8.

TABLE 3-3 Sample 12 Sample 13 Surface Area (m²/g) 8.9 11.4 PSD Cilas d90(um) 2 N/A Cilas d50 (um) 0.5 N/A

TABLE 3-4 Sample Id: SiO2 Al2O3 Na2O TiO2 Fe2O3 MgO CaO LOI Sample 120.03 99.8 0.07 N/A 0.02 0.05 0.02 N/A Sample 13 60.4 0.30 0.18 <0.1 1.4031.7 0.25 5.20

The raw material batches were extruded using a piston extruder to formsolid rods. The samples were dried initially at 110° C. in a dryingoven. Samples were then fired in a high temperature furnace using a ramprate of 5° C./min to 1280° C. with a hold time of 1 hour to producestoichiometric cordierite. The coefficient of thermal expansion (CTE)for the three cordierite samples was measured using an Orton Model 1600dilatometer (Table 3-5). Sample 9 produced using the novel kaolin blendof a fine, hydrous and a coarse, delaminated kaolin (Sample 6) resultedin a CTE of 2.7×10⁻⁶ as compared to the control cordierite Samples 10and 11 produced using Kaolin Samples 7 and Sample 8. This was areduction in CTE of 60% demonstrating the ability to improve thermalperformance in cordierite ceramic bodies and substrates through the useof the novel kaolin blend.

TABLE 3-5 Temp. Sample CTE (10⁻⁶/K) Range (° C.) Sample 9 2.7 400-800Sample 10 6.8 400-800 Sample 11 6.8 400-800

While the present invention has been particularly described, inconjunction with a specific preferred embodiment, it is evident thatmany alternatives, modifications and variations will be apparent tothose skilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives, modifications and variations as falling within the truescope and spirit of the present invention.

The invention claimed is:
 1. A method of making cordierite comprising:mixing, extruding and sintering a cordierite precursor comprising ablended hydrous kaolin clay product comprising (a) a platy coarse kaolinclay having a mean particle size of less than 2 μm in diameter; and (b)a fine, hydrous kaolin clay having a mean particle size of less than 1μm in diameter, wherein the blended hydrous kaolin clay product has atotal particle mass where more than about 75% and 86% or less of thetotal particle mass is less than 2 μm as measured by a Sedigraph 5100.2. The method of claim 1, wherein the platy coarse kaolin clay isdelaminated kaolin clay.
 3. The method of claim 1, wherein the weightratio between the platy coarse kaolin clay and the fine, hydrous kaolinclay is between about 10:90 and about 90:10.
 4. The method of claim 1,wherein the weight ratio between the platy coarse kaolin clay and thefine, hydrous kaolin clay is between about 50:50 and about 90:10.
 5. Themethod of claim 1, wherein the weight ratio between the platy coarsekaolin clay and the fine, hydrous kaolin clay is between about 70:30 andabout 90:10.
 6. The method of claim 1, wherein the platy coarse kaolinclay is a Cretaceous or secondary clay and the fine, hydrous kaolin clayis clay mined from tertiary crude deposits.
 7. The method of claim 6,wherein the impurity profile for the blended clay product is less thanabout 0.1% Na₂O, less than about 0.25% K₂O, less than about 1.75% TiO₂,less than about 0.6% Fe₂O₃, less than about 0.1% CaO, and less thanabout 0.1% P₂O₅ by weight.
 8. The method of claim 7, wherein the weightratio between the tertiary crude deposits clay and the Cretaceous orsecondary clay is between about 90:10 and about 10:90.
 9. The method ofclaim 7, wherein the weight ratio between the tertiary crude depositsclay and the Cretaceous or secondary clay is between about 50:50 andabout 10:90.
 10. The method of claim 7, wherein the weight ratio betweenthe tertiary crude deposits clay and the Cretaceous or secondary clay isbetween about 30:70 and about 10:90.
 11. A method of forming a blendedhydrous kaolin clay product, the method comprising blending clay minedfrom tertiary crude deposits as a fine component with a Cretaceous orsecondary clay, wherein the Cretaceous or secondary clay is a platycoarse kaolin clay having a mean particle size of less than 2 μm indiameter; and the fine component is a fine, hydrous kaolin clay having amean particle size of less than 1 μm in diameter, and wherein theblended hydrous kaolin clay product has a total particle mass where morethan about 75% and 86% or less of the total particle mass is less than 2μm as measured by a Sedigraph 5100.